Air purification device



April 22, 1952 H. F. FRUTH 2,593,869

AIR PURIFICATION DEVICE Filed July 15, 1948 [n z/emor Hal Frederick HuiPatented Apr. 22, 1952 UNITED STATES PATENT OFFICE Hal Frederick Fruth,Skokie, 111.

Application July 15, 1948, Serial No. 38,882

3 Claims. (Cl. 183-7) The present invention relates to air purifiers andmore particularly to means for ionizing airborne particles preparatoryto precipitating them on charged collector plates.

It is an object of the present invention to provide improved means forcharging suspended dust and the like by the action of an electrodecontaining a material capable of emitting charged particles into the airstream. It is a more detailed object to provide an improved electrodeconstruction to facilitate the emission and acceleration of ionsenabling precipitation of pollen and other microscopic dispersions aswell as large particles of dust and the like. Still another object is toprovide an ionizer which is simple and inexpensive and suflicientlydurable to withstand rough usage in domestic and industrial airconditioning applications.

Other objects and advantages of the invention will be apparent from thefollowing detailed description taken in connection with the accompanyingdrawings, in which:

Figure 1 is a schematic view showing an air duct and collector platesand illustrating the manner in which ionizing electrodes are associatedtherewith.

Fig. 2 is a fragmentary view showing on an enlarged scale the detailedstructure of an electrode, fabricated in accordance with the invention.

Fig. 3 shows a transverse section of the electrode of Fig. 2 togetherwith an adjacent electrode of opposite polarity.

While the invention is susceptible of various modifications andalternative constructions and uses, I have shown in the drawings andwill herein describe in detail one embodiment of the invention. It is tobe understood, however, that I do not intend to limit the invention bysuch disclosure, but aim to cover all modifications and alternativeconstructions and uses falling within the spirit and scope of theinvention as expressed in the appended claims.

Referring now to the drawings, Fig. 1 is a diagrammatic view showing anair duct ID, a set of oppositely charged collector plates I I, andionizing electrodes indicated generally at l2. Conventionally, alternateones of such electrodes are connected in sets [4, 15 to a source of highpo tential so that the resulting brush or corona discharge causessuspended particles in the immediate vicinity of the electrodes tobecome ionized and therefore attracted to the charged collector plates.In this instance a positive charge is applied to the electrodes l5 and anegative charge is applied to the electrodes M. Tests have shown thatthe degree of ionization attainable in this manner using moderatevoltages is small and that a very elaborate arrangement of precipitatorplates is necessary in order to insure that a high percentage of thesuspended foreign matter is removed from the air before it is againdischarged into the air-conditioned chamber.

In accordance with the present invention, the degree of ionization isgreatly increased by an improved physical construction of the ionizingor negatively charged electrodes I4 and by including therein certainionizing substances capable of emitting charged particles, primarilyelectrons.

As shown, each electrode l4 comprises a stringlike body 28 having frayedstrands 29 of conducting Wire or the like projecting from the surface ofthe body in closely spaced relation to each other. The electrode body 28is formed from thermally non-conducting material and in this instanceconstitutes a frayed strand of woven or spun yarn composed of glass ortextile fibers. A layer of conducting material is deposited on thesurfaces of the electrode body and the projecting strands 29. Thissurface layer may, for example, consist of an electrically deposited orchemically reduced layer of aluminum, magnesium, or zinc.

If desired, however, and without departing from th invention one or moreof the following metals may be employed in the formation of this coatinglayer: beryllium, calcium, zinc, strontium, cadmium, and barium, allfrom group II of the periodic classification. Caesium from group III andthorium from group IV may also be successfully used. The metals need notbe in their metallic state since the characteristic low work functionmay also be obtained using the metals in the form of compounds such asthe oxide formed in situ.

When potential is applied between a negative electrode I4 and anadjacent positive electrode or rod [5, an electrostatic field is set up.The positive rod I5 is preferably smoothly rounded and consequently mostof the potential drop occurs in the vicinity of the sharp points of thefrayed strands 29. Due to the resulting high gradient, electrons arefreed from the points of the strands and are rapidly accelerated in thedirection of the adjacent electrode l5. Because of the large number andspeed of the electrons, efficient ionization is produced causingeifective precipitation of particles over a wide range of sizes. Byusing an emitting electrode of the above type it is possible to employvoltages much 3 lower than conventionally required without sacrificingprecipitation efficiency. Thus the production of ozone may be keptwithin reasonable bounds and the disagreeable physiological effectsassociated therewith completely eliminated.

The coated projecting strands 29 of the electrodes I4 are poor thermalconductors. Thus, by proper spacing of the electrodes i4, 15, the flowof current may be adjusted so as to cause heating to take place at thetips of the projecting strands. The latter is apparently due to positiveion bombardment as well as electron flow. This has been found to greatlyincrease the facility with which the electrons are emitted and increasesthe total number of electrons available even at moderate ionizingvoltages. While a number of diiferent alloys may be employed having thedesired emissive properties as mentioned above, it is preferable toselect one having at the same time a high resistance to continuedoxidation and not subject to appreciable loss as a result of cathodesputtering. Alloys having the wear characteristics of magnesium-aluminumalloy are preferred because of the thin self-protecting oxide coatingformed on the surface. Although the invention has been described asparticularly suited for use with direct current, it will be understoodthat alternating current is also suitable, each electrode beingfabricated similarly to the electrodes I4 and serving asv a cathode forhalf the time.

To further increase the electron emission of the electrodes M, aconductive coating is used containing radioactive material. The lattermay consist of a dispersion of radium, polonium, uranium, or the like,but preferably less expensive materials are used which have been madeartificially radioactive by bombardment. Examples of such materials arethe following radioisotopes and compounds containing them: strontium 90,carbon 14, chlorine 36, technitium 99. These have sufficient emission ofelectrons (beta radiation) to give increased ionization and have ahalf-life of at least twenty-five years. Due to the substantial absenceof gamma radiation there isno danger that harmful radioactivity'will beimparted to the air.

In the foregoing discussion the efficiency of the present electrodeconstruction and arrangement has been discussed particularly as regardsthe charging of larger air-borne particles preparatory to theircollection by the collector plates. Studies have shown that thearrangement disclosed herein possesses practical advantages not to befound in prior art ionizing devices. I have found, for example, that thearrangement is particularly effective for removing particles. ofextremely small size, for example, such as pollen grains, bacteria andfiltrable viruses. As a result, the precipitator including the presentionizer is extremely valuable to hay fever sufferers and for germicidalpurposes-in hospitals, laboratories and the like.

What is claimed is: i

1. A precipitating device for ionizing air-borne particles including, incombination, two ionizing electrodes disposed in spaced relation to eachother, one of said electrodes comprising an elongated body formed frominterlaced fine strands of yarn having high electrical and heatinsulating properties, said body being of sufficient strength to beself-supporting between its ends, the surface of said body being frayedso as to present a large number of closely spaced outwardly extendingprojections of said fine strands of yarn, and a fine coating of electronemissive metallic material on the surface, of said body and on saidprojecting strands of yarn, the strand projections thus coated havingsubstantial length but being of small transverse cross section, saidcoated strands having both good heat insulating properties and goodelectrical conducting properties, the ends of said projectionspresenting minute electron emitting points which become heated tohigh-temperatures when said device is in operation.

2. A precipitating device for ionizing air-borne particles comprising,in combination, two ionizing electrodes disposed in spaced relation toeach other, one of said electrodes comprising an elongated body of heatinsulating material, a pluralityof fine strands of material including atleast one component of substance having good electron-emittingqualities, said strands having closely spaced relation to each other andprojecting outwardly in random directions from the surface of saidinsulating body to present a. large number of minute electron emittingpoints disposed on the ends of relatively long but thin supportingmembers having very small transverse cross sections.

3. A device as set forth in claim 2 in which said electron-emissivesubstance of said strands constitutes radioactive material.

HAL FREDERICK FRUTH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 617,618 Thwaite Jan. 10, 1899945,917 Cottrell Jan. 11, 1910 1,067,974 Cottrell July 22, 19131,357,201 Nesbit Oct. 26, 1920 1,399,422 Chubb Dec. 6, 1921 1,409,901Anderson Mar. 21, 1922 2,231,330 Gove Feb. 11, 1941 FOREIGN PATENTSNumber Country Date 338,796 Great Britain Nov. 27, 1930 816,463 FranceMay 3, 1937 425,273 Germany Feb. 16, 1926 442,644 Germany Apr. 2, 1927507,914 Germany Sept. 22, 1930

